1. Field of the Invention
The present invention relates to optical metrology, and more particularly to improving the accuracy of measurements made using optical metrology. The present invention relates to a method and apparatus for improving the optical properties of 243 nm soft masks, 193 nm soft masks, 157 nm soft masks, extreme UV soft masks, x-ray wavelength sensitive soft masks, and electron beam sensitive soft masks to improve the accuracy of lithographic features and critical dimensions.
2. Description of the Related Art
Optical metrology involves directing an incident beam at a structure, measuring the resulting diffracted beam, and analyzing the diffracted beam to determine various characteristics, such as the profile of the structure. In semiconductor manufacturing, optical metrology is typically used for quality assurance.
In general, photoresist compositions comprise at least a resin binder component and a photoactive agent. Photoresist compositions are described in Deforest, Photoresist Materials and Processes, McGraw Hill Book Company, New York, ch. 2, 1975 and by Moreau, Semiconductor Lithography, Principles, Practices and Materials, Plenum Press, New York, ch. 2 and 4, both incorporated herein by reference for their teaching of photoresist compositions and methods of making and using the same.
For example, after fabricating a periodic grating in proximity to a semiconductor chip on a semiconductor wafer, an optical metrology system is used to determine the profile of the periodic grating. By determining the profile of the periodic grating, the quality of the fabrication process utilized to form the periodic grating, and by extension the semiconductor chip proximate the periodic grating, can be evaluated.
Conventional optical metrology can be used to determine the deterministic profile of a structure formed on a semiconductor wafer. For example, conventional optical metrology can be used to determine the critical dimension of a structure. However, the wafer may be formed with various processing effects that can decrease the accuracy of the optical measurements.